The present invention relates to an image display device of the panel type which utilizes the birefringence properties of a ferroelectric material.
Many attempts have hitherto been made in panel type image display devices to improve their operating characteristics to meet the requirements of television systems. These devices include plasma display, liquid crystal display, electroluminescent display and electrochromic display panels. However, such displays have various limitations in performance and production. For example, plasma display devices, although satisfactory in color separation, have high operating voltages which make it difficult to design a compatible control circuit and adds complexity to production process. Electroluminescent displays are similarly operated on high voltages, and color rendition (except for orange) is poor. Liquid crystal and electrochromic display panels have limitations in response characteristics and excessively high temperature dependent characteristics.
Attempts have also been made recently to utilize the light scattering properties of a transparent ferroelectric material such as lead lanthanum zirconate titanate (PLZT) ceramic in panel display applications. The light scattering properties of the ceramic material are attributed to a change in crystal structure of the material under the influence of an electric field applied in the direction of thickness of the material. For example, a PLZT ceramic plate having a thickness of 200 micrometers requires the application of 200 volts or more to produce crystallographic structural change. Since conventional integrated circuits which are extensively used in various applications operate on voltages much lower than 200 volts, the electrode control circuit would require specially designed integrated circuits, resulting in an increase in production cost.
Another type of image display device is one which utilizes the birefringence properties of ferroelectric material. Such an image display device comprises first and second polarizers having their planes of polarizations oriented at right angles to each other and an electrooptic plate interposed between the polarizers with an electrode matrix being secured to the electrooptic plate. Although this birefringence type of display compares favorably with the light scattering type in terms of image contrast, undesirable "cross-coupling" occurs between non-selected matrix electrodes which tends to degrade the sharpness of reproduced images.